When a creature from a planet other than Earth looks like a human, sounds like a human, acts somewhat like a human and gets confused for a human.

Their internal physiology may well be different, whether a little or a lot or just none, but otherwise they appear to be the genuine article.

In-story, this occasionally leads to a Handwaving story about how all the races have some common ancestor. Other times, it gets justified by using a Transplanted Humans story. Out-of-story, this is often explained by the fact that there are remarkably few non-humanoids in the SAG or Equity. Other explanations include the idea that a humanoid form is the natural result of any evolutionary path (Humans Are SpecialonEvolutionary Levels). Recent research hints at this being true to some extent; many species seem to be engineered by evolution for maximum fuel efficiency. The bipedal human body has remarkable agility and stamina for its size. Although there are some notable flaws like weak joints and a narrow birth canal, our impressive cognitive abilities and incredibly complex social structure evolved to counter these. There's also a real phenomenon known as "Convergent Evolution" whereby species that originated in different areas eventually develop into things that look similar because it's a useful form.

In 1950's movies, this also could be used as an actual part of the theme of the story, as the idea that these sorts of aliens could pass completely for humans made a rather handy metaphor for Communism.

Technically there could be another rung below this one on the Alien ladder: Caucasian Aliens. There are many fictional planets where the aliens not only look human, they are all Caucasian-looking. This is rife with Unfortunate Implications. The opposite situation, where the alien race is genuinely alien, but they are all African-looking, or Asian-looking, etc., is vanishingly rare (and would probably carry a different batch of Unfortunate Implications).

The Zentraedi of Macross/Robotech and its descendants are one of the clearer examples of the trope, straight down to the Hand Wave concerning their origins being linked to that of humanity. The primary physiological difference being that in their natural state they are ten meters tall, but can through an ill-defined process be shrunk down to roughly human size (or expanded back up).

The Buff Clan in Space Runaway Ideon look identical to humans, with the exception of them lacking pupils. They also possess the honor code of the samurai, call their warriors samurai (though the actual humans don't), and even call their home planet Earth. If it weren't for the fact that they were an isolated race before meeting the people of Logo Dau, you'd swear that they were human!

The aliens who inhabit the world of Simoun are all mostly human, except that they're all born female, and half of them change sex at age 17.

Well, technically they are all born neuter with external female traits, like ant drones, and only get actual gender-properties at the age of 17, namely the ability to procreate, either as males or females.

The natives of The Twelve Kingdoms seem almost indistinguishable from humans of Earth stock, but in fact have a bizarre life cycle that includes being born from large fruit that grows on special trees.

Similar to the Saiyans above, Lala's race from To LOVE-Ru are indistinguishable from humans apart from their tails. In a similar vein, there is Ren/Run, whose only difference from humans is his uncontrolledGender Bending. There are other examples of Human Aliens, but it is shown that there also exist Rubber Forehead Aliens and Plant Aliens, so at least the universe has some variety.

The S and Stars seasons of Sailor Moon brought so many Human Aliens (or at least aliens that were originally human in appearance) from across the galaxy to Tokyo that one could wonder if non-humanoid intelligent lifeforms really existed at all! Even the talking cats Luna and Artemis, who were aliens from the planet Mau in the manga, could assume human forms. (Rei's crows Phobos and Deimos were also revealed to be aliens who could take human form in the manga.) The filler arc villains Eiru and An from the start of the second season were also aliens who could assume human form, though the villains from the first season and the rest of the second season were originally from Earth.

The Moon Kingdom inhabitants and the Senshi of the past could also count, since they're technically not from Earth. This also means Queen Nehelenia/Zirconia, the Big Bad from SuperS, would count, even though the rest of her minions are either from Earth originally (animals given human form, some girls from the rainforest given powers) or are dream-monsters (the Lemures).

The Plants in Trigun look exactly like humans, all to various degrees. The ones used as power look semi-humanoid with wings and other assorted appendages, while Vash and Knives can easily pass for human. This is because plants were made by humans.

In the manga however they are beings from another dimension with different laws of physics which is why they can generate power from seemingly nowhere. In their default state they also look something like a human glued to a bunch of baby corpses, tumors, and angel wings.

The Juraians in Tenchi Muyo! not only look human but have Japanese-sounding names. According to Ayeka's computer in the first episode of the OVA Earth is a 'colony world' seemingly suggesting that humans are actually transplanted Juraians. Unfortunately the matter is never explored beyond that one throwaway comment.

The Nazi-inspired Gamilons from Space Battleship Yamato / Star Blazers began as looking identical to humans in every sense of the word. However, the creators of the show retconned their design a few episodes into the show and gave them blue skin, blonde hair and black eyes. Why? Probably to distinguish them easily from the human cast.

This is further developed when it's discovered that the Gamilons need radiation to survive, like how a human needs oxygen to breathe.

When the crew captures its first Gamilon prisoner and sees what their opponents look like, this is a huge shock for them, as they'd pictured the Gamilons as monsters. It plays into the theme of the episode, as well, as Wildstar / Kodai must put aside his overwhelming hatred of the aliens who killed his family to see this prisoner as a person who should be treated decently.

Lum and her family in Urusei Yatsura look almost exactly like humans, only with two small horns. However the series does feature other aliens in all shapes and sizes.

In the series Inuyasha, it's the Yokai who look human who are considered most powerful.

A similar notion extends to Yu Yu Hakusho, as quite nearly all of the show's most powerful demons appear human.

Jumping on the bandwagon, the Hollows/Arrancars in Bleach follow this trend as well.

While not aliens, the main characters of Wolf's Rain spend a lot of time looking human, mainly as a form of camouflage, as they're supposed to be extinct.

Mahou Sensei Negima has an interesting take on this, in that the Magic World is in Another Dimension, that happens to be layered on top of Mars. Meaning that anyone from the magic world is technically an alien.

Background material indicates that the Mu evolved on Earth alongside humanity, so it's possible that they aren't a different species at all, but merely another race of humanity... which would turn this example into a Subversion.

Bakugan Battle Brawlers New Vestroia introduces an extra-dimensional race known as the Vestals. There's not much difference between humans and Vestals, aside from their eyes. Human eyes have distinct, black pupils, while the Vestal pupil is just a darker shade than their iris. Given this style of pupil can be the norm for humans in other shows, one might not notice the difference immediately.

The aliens from Niea7 are human for all practical purposes, save for the shape of their ears and conspicuous antennae (for most of them) on top of their heads. Chada is somewhat of an exception, since he is plain ... weird.

Those are the Humanoid Interfaces created by the actual Starfish Aliens who are so alien that they don't even seem to have physical forms. Technically Yuki and the others are gynoids, and not aliens themselves.

Though there are apparently enough differences that Birdy in the remake manga had to warn Tsutomu to avoid the hospital lest abnormalities be detected.

The Coralians in Eureka Seven are born with various shapes and sizes for their forms, including human Coralians like Sakuya, Eureka and Gonzy.

Justified in that they were created to look that way.

Haruko Haruhara from FLCL... maybe. She claims to be a 19-year-old space patrol officer, but is actually a galactic criminal out to find the Pirate King Atomsk. Its kinda hard to be sure of anything Haruko tells anybody. Other than pink hair and yellow eyes, Haruko is entirely humanoid. Also she fights with a Rickenbacker guitar, uses a house cat as a walkie-talkie, and has a flying Vespa.

She can change her voice and probably appearance at will, as seen in episodes 1 and 5, which puts her in the A Form You Are Comfortable With category. Which would also explain what happens to her face when she's angry.

In World of Narue, Narue is half-alien half-human, but her father, sister, and all other members of her species look completely human. They also come from planet Japan, which also appears to have a history very similar to the Japan we know, so go figure.

In Asobi ni Iku yo!, not only do the Catians look exactly like humans except for the cat ears and tail, they even called their planet "Earth" until they decided to make contact with us, then re-named it to Catia for our convenience. This seriously ticks off Beautiful Contact, a group of hardcore sci-fi fans who insist that humanity's First Contact with an alien species should be with a race that looks more dignified and unearthly.

Not surprisingly, the same trope is in effect for Ichika Takatsuki in the third show in the same universe, Waiting in the Summer.

The Yato from Gintama appear very human, although they do have super strength and are weak to the sun. Even their coloring isn't unnatural—Kagura and Kamui's orange hair and blue eyes would be uncommon in Japan, but have been seen elsewhere. Other Yato characters are shown with even plainer coloring.

The aliens of Please Save My Earth are only the size of a human thumb, but look exactly like humans.

Superman, Supergirl, and all other Kryptonians are outwardly indistinguishable from humans, despite obvious biological differences. Exactly how close or distant humans and Kryptonians are can vary depending on the work:

According to some Silver Age stories, Kryptonians were descendants of humans plucked from Earth by a more technologically advanced race. Some Post-Crisis stories imply this as well.

One Superman/Flash story has the duo facing a mysterious alien race that apparently seeded both Earth and Krypton with life, at around the same time, serving as a possible explanation for this trope.

It is mentioned that Jor-El chooses Earth because humans looks exactly like Kryptonians, so Kar-El could live among them without detection.

Lampshaded in an issue of Starman where Jack Knight's journeys through space and time land him on Krypton before its destruction. He is promptly arrested by the authorities, who suspect him of being a member of a Kryptonian rebel group. When Jack tries to argue that he's an alien visitor from planet Earth, his interrogator refuses to believe him, pointing out that he looks no different from any Kryptonian. Jack wonders whether God was feeling unoriginal.

Other stories suggested that the human and Kryptonian species actually were directly related:

Krypton dodges the Caucasian Aliens trap via "Vathlo Island", home to "a highly developed black race" of Kryptonians, first mentioned in 1971.

There's a very strong tendency for aliens in The DCU to look exactly like humans:

In Legion of Super-Heroes, most of the alien races are perfectly humanoid in appearance, although they possess various additional abilities. Post-Crisis, this was handwaved by having them be descendants of humans who were given superpowers in alien experiments (this explanation was later Ret Conned out of existence by the 2010 "New Krypton" storyline, which tells us they were, in fact, alien races to begin with.)

Natives of Rann seem to be entirely indistinguishable from humans. Indeed, human hero Adam Strange had a child with his Rannian wife Alanna.

Blackest Night revealed that Earth was really the place where life began, which might help explain all the humanoid life in the galaxy.

The planet Bellatrix from the Green Lantern series has a very human-looking population, but with a refreshing amount of diversity. One of the planet's two Lanterns, Zale, fits this trope, looking like a human of African descent.

The Kree are divided into two races: the pink Kree, who look just like Caucasian humans, and the blue Kree, who look just like humans, save for their blue skin.

Karolina Dean of Runaways looks exactly like a normal human as long as she wears a bracelet made from a special material that dampens her powers. When she takes the bracelet off, she looks more like a human-shaped beam of multicolored light. It turns out that her parents come from the planet Majesdane.

In a similar manner to Superman, the Viltrumites of Invincible, of whom main character Mark is a human hybrid, are basically humans with superpowers, and, if they're male, mustaches. All of them. And that's it.

The Wildstorm Comics 'Verse has Kherubim, super-powered humanlike immortals who can even interbreed with homo sapiens. It's eventually revealed that this is because Earth and other planets were seeded with devices designed to spread the Kherubim genome across the universe in a form of bloodless conquest. Not that they were averse to the bloody kind on occasion either, being a Warrior Race.

The many worlds of the Cross Gen universe seem quite prone to humanity as a dominant population. Possibly explained by Geromi in Crux, who mentions a mass exodus from Earth at some point that led to many other worlds being colonized, and that nobody's a true human any more. Discussed in the world-hopping storylines of Sigil and Mystic, when Sam and Giselle encounter humans on a variety of strange worlds (in fact, it initially takes Giselle a while to realize she's not on Ciress any more).

All the alien races in The Chronicles of Riddick series. This gives the superficial illusion of Absent Aliens, but there are a few here and there revealed to be aliens. Such as the air elemental, who looks like a normal old lady Dame Judi Dench, but can turn into mist as she chooses. And there's the protagonist, Riddick, who's Furyan.

Although neither are positively identified as aliens; the Elementals may simply be humans who have developed certain skills or been modified in some unexplained, apparently supernatural way - this apparently being possible in the Riddick Universe, judging by the Lord Marshal - and it is never explicitly stated whether the Furyans are an alien race, or merely a particular human population. In the Alan Dean Foster novelization Furyans are simply humans from a world of high gravity and Riddick is the last one, explaining his strength and speed on worlds with lower gravity.

Thomas Jerome Newton in The Man Who Fell to Earth is actually a Rubber Forehead Alien, but appears human (as human as David Bowie is capable of looking, at least) throughout most of the film through the use of contact lenses and stage makeup, as well as a few prosthetics for other parts of his body. Without his cosmetics, his bright golden skin and eyes with vertical, ovular pupils would give him away. Biologically his people are similar to humans, but among other things have longer life spans (Newton remains the same age while other characters in the movie go from college age to their late 50s) and are extremely sensitive to X-rays (even more so in the source novel, in which they prove blinding).

The squid-like Thermians in Galaxy Quest use appearance generators to look human. Somewhat justified: they based their entire society and technology on a human TV show, and they were trying to fit in with their human guests. Since they have no concept of deception, it isn't meant to let them pass for human or even to make the humans ease into the whole alien thing; it's just their version of Cosplay.

Also, the Thermians built their Protector to look and control exactly like the one they saw on TV... which left them with a machine wholly incapable of being controlled by their actual bodies. They need human-shaped hands to use the ship!

Star Wars, of course, features Human Aliens alongside Serkis Folk. There's no sign of Earth, and what connections or differences exist between the totally-human-looking races of different worlds remains unknown. (One must wonder if there are other planets with, say, Wookiees that are completely unrelated to the ones of Chewie's homeworld of Kashyyk...)

Most sources which dwell on the subject imply that Coruscant is the human homeworld, but no one knows for sure. The other humans are the result of sleeper ships launched before the founding of the Galactic Republic or of Precursors moving them around as slaves. After the founding of the Republic (most of whose members were the result of the sleeper ships) widespread colonization ensued using the hyperdrive.

Knights of the Old Republic implies that the human homeworld was actually Tatooine. The originals were the ancestors of the Sand People as well, who abandoned technology after a (technically) successful rebellion against the Rakatan that also led to the world being turned into a desert by orbital bombardment.

When C-3PO introduces himself, he always adds, "human-cyborg relations". It seems they are human after all. Then again, he's not a cyborg.

The Lost Skeleton of Cadavra used this trope with the "Marvans" as part of an affectionate spoof of low-budget sci-fi horror movies from the 50s.

Lattis:It's interesting how different people from different planets differ.

Robert Rankin shamelessly lampshades this in one of his stories (Armageddon, the Musical I think) where it is advanced as proof that there is a God who designs dominant species in his own image. "As any Science Fiction fan knows, the basic human shape, Head at the top, two feet at the bottom, wedding tackle about halfway down, is the standard for intelligent life the universe over. They often speak good English with a noticeable American accent, too. Facts that should serve up friend Atheist with a workload of eggs, faces for the use of."

In one Discworld book (though it was referring to gods, the spirit's the same), it's mentioned that if you ask someone to come up with an alien-looking being, it would basically be a man in an animal mask.

The Takisians of the Wild Cards series. In fact, that's what leads to the entire plot of the series; the Takisians note how biologically similar they are to humans, believe they must be the descendants of a "lost colony," and drop the wild card virus on Earth to test out its purpose as a biological weapon.

The various biological species of The Culture are mostly human-looking, although they have various additional internal glands and bits. Given the degree of casual genetic modification in the universe though, it's anyone's guess as to whether they were all always like that.

In The Use of Weapons, Shias Engin asks Zakalwe "I know that all the outworlders aren't humanoid, but a lot are. How come?". Zakalwe replies jokingly that it is the universe's way of getting rid of alcohol.

Some of them are human, a result of The Culture grabbing some of them to spread out across the universe.

Now, in all the above, there are two untold stories implicit. One is the history of the Culture's formation, which was a lot less easy and more troubled than its later demeanour might lead one to expect, and the other is the story which answers the question; why were there all those so-similar humanoid species scattered around the galaxy in the first place?
Each story is too complicated to relate here.

In Ursula K. LeGuin's series the Hainish Cycle, this is because all the humanoid races are from planets colonized by the titular Hainish. Including Earth humans. Despite a common ancestry, they don't all look like us. The Cetians are hairier, for example, and the Athsheans are green (fairy green, not Martian green) and diminutive.

In James Patterson's The Dangerous Days of Daniel X, the aliens on Daniel's home world, Alpar Nok, look exactly like humans. The planet even looks like Earth.

In the Perry Rhodan universe, the ancestors of the most prominent 'human alien' races of our galaxy actually came from Earth. (Extra irony points for one of those species later coming back and, quite unaware, claiming 'Larsaf III' as a colony of their own for a brief time.) Humanoid life in general seems to have some common ancestors in the distant cosmic past, and can also be partially justified by the fact that Sufficiently Advanced Aliens have been known to meddle in the evolution business as well.

Jadis in the Narnia series may also qualify, as God in this series has created nearly identical animals on other worlds. This also results in such things as Bear Aliens and Mouse Aliens. On the other hand, Jadis may be descended from Transplanted Humans, like the Narnians.

The beavers in The Lion The Witch And The Wardrobe claim she was descended from Lilith, which just raises further questions. Of course, they aren't exactly experts on Jewish apocrypha.

Specifically, she is claimed to be descended from the Djinn on one side of her family, and the Giants on the other, and to have no human blood at all. One of the themes in the books is that being that look like humans but aren't are, invariably, wrong in ways that make them inimical to humans.

The Noon Universe novels of the Strugatsky Brothers feature a lot of Planet of Hats Human Aliens civilizations, though their cultural, technological and historical development is rarely 100% identical to that of the Terrans. Among the most inventive examples are the people of the planet Saraksh, whose entire philosophical and religious system has been heavily influenced by the immense optical refraction phenomenon present in the atmosphere of their homeworld. From the surface it looks like the horizon is above the observer, which makes the Sarakshans think that they actually live inside a hollow cave in an endless piece of rock, rather than on a round planet floating in space. They call all who claim otherwise "Massaraksh" ("of the world inside-out"), a term which is also an Unusual Euphemism for "insane".

Then there are the Leoniders, who are essentially a whole race of Space Amish.

Justified in Sergey Lukyanenko's A Lord from Planet Earth trilogy, where all races in the Milky Way (except humans) have been seeded by a mysterious precursor race. Played straight with Human Aliens from a faraway galaxy.

Thomas in The Man who fell to Earth.

In Sergey Volnov's Army of the Sun trilogy, there are three alien races who are dead ringers for three of the major human "sub-races" (the term used in the books): whites, blacks, and Asians. Nobody knows why that is the case, although there are plenty of other humanoid races. The leading theory is that they have been transplanted to other planets from Earth by Precursors. This theory is partially supported by several ancient records of the "Asian" race that look eerily similar to Ancient Chinese. To top it off, the name of their legendary ancient leader is very similar to "Genghis Khan". In any case, during the centuries of galactic domination of the EarthStella Empire, these three races were shown preferential treatment due to their, at least external, similarity to humans. After the aliens rebelled (justified, as Imperial humans were bastards), they killed off many humans and enslaved many others. Those who survived and were not enslaved are still treated as second-class citizens (if that). As such, most traveling humans tend to pass themselves off as members of one of these human-like races, as aliens have no beef with them.

This is the whole point of Zenna Henderson's The People. They may be from a galaxy far, far away and have godlike paranormal abilities, but they look exactly like us. (In one story, "Deluge", there's a hint that they may have changed some to match Earth's environment.)

The Elyins and the Kin in Geary Gravel's 1984 novel The Alchemists.

Parodied in The Star Diaries by Stanislaw Lem, where a group of Starfish Aliens living on an extremely hot planet discuss a possibility of an intelligent species living in a lower temperature; the oldest one explains that the existence of such creatures is impossible, and any other sapient species must be exactly like them. While Lem used the trope in comedic works, he criticized its use in serious ones.

Doctor Who did this more times than can be counted. The most famous examples are, of course, the Doctor himself and the other Time Lords. Their most noticeable physiological differences (two hearts, 60-degree Fahrenheit body temperature, a far more complex brain structure, a respiratory bypass system, "symbiotic nuclei" in their cellular structure, and whatever organs or systems are responsible for their ability to regenerate) were effectively invisible to the television viewer.

The Expanded Universe did a Lampshade Hanging by having a racist founder of Time Lord society, who thought that the Time Lord form was supreme to any other, go around the universe and infect species with a virus that would cause them to evolve into humanoid forms.

Earlier, the Expanded Universe lore had come up with a completely different Lampshade Hanging, also involving the Time Lords. The Time Lords evolved first out of all sentient species. Therefore, the morphic resonance of Time Lord-ness propagated throughout the universe.

Yet another lampshade was hung in the Easter 2009 special Planet of the Dead. A similar conversation between Amy and the Doctor was repeated in "The Beast Below", the following year.

A similar situation does appear in the Slitheen two-parter "Aliens of London" / "World War III" where Mickey asks Rose how she doesn't know the doctor isn't just wearing a human suit like the Slitheen.

This comes up in the classic series as well, most notably in 1973's Carnival of Monsters, where a travelling Lurman showman named Vorg remarks upon the strong resemblance between his species and the human race (known to him as Tellurians):

Vorg: These creatures are Tellurians, a species discovered in a distant galaxy. Scientists have been amazed at the remarkable similarity between these little chaps and our own dominant lifeform.Orum: The resemblance is unpleasant.Vorg: These are the only Tellurians in captivity. Some scientists think that their discovery refutes Valdek's theory that life in the universe is infinitely variable.

Thals and Kaleds look like humans. "The Stolen Earth" reveals that they have fewer ribs than humans and Bizarre Alien Biology, though.

According to the audio drama I, Davros: Corruption, Kaleds and Thals were separate species who both evolved (on the same planet, obviously) to a humanoid form as that is the optimum biological form for Earth-like planet. One of the novels in the Doctor Who Expanded Universe made a similar claim about all human like species which may or may not contradict the explanation given above relating to the Time Lords.

The Fifth Doctor had quite a few non-Time Lord Human Alien companions, to the point where it gets a bit of a Lampshade Hanging in Four To Doomsday. Tegan mentions that she's human, and their alien hosts ask if the rest of them are too. The Doctor has to correct them that, no, he's from Gallifrey, Nyssa is from Traken and Adric is from Alzarius. Turlough from Trion joins the TARDIS the following season, just to top it all off.

In the 2007 Christmas special "Voyage of the Damned", everyone seen on board the Titanic (a starship moulded into a replica of the 1912 ship) apart from two cyborgs are indistinguishable from humans, yet know very little about Earth culture, even the self-proclaimed Earth expert.

Star Trek: The Original Series had several, and it was rather strange when Spock was the only crew member who had to disguise himself on an alien planet. (It was even stranger when Kirk's Beleaguered Childhood Friend was able to make himself dictator of an alien planet without any of the aliens noticing something odd about him.) In fact, aliens are Human Aliens more often than not, probably for budgetary reasons.

One comment by Spock during the first season suggested that his species and many other humanoids were created by a superior race and it was part of his planet's mythology. This explanation seems to have been dropped in favor of one in which a race of Precursors seeded DNA with code to create humanoids in Star Trek: The Next Generation.

Star Trek: The Next Generation attempted to provide an explanation for the prominence of humanoid species (both Human Aliens and Rubber Forehead Aliens) in the universe by revealing that there was a common ancestor race that "seeded" the galaxy with its basic genetic material. They switched to exclusively using Rubber Forehead Aliens rather than Human Aliens after the first few seasons (excluding Guinan's people, the El-Aurians and Councelor Troi's, the Betazoids).

Star Trek: Voyager had a few Human Aliens in its first season, too, mainly wearing strange and colourful national dress.

At least Star Trek: The Original Series had a few attempts at using body paint for doing alien skin colours. Voyager had an absurd number of aliens who were virtually indistinguishable from humans, even in later seasons when they had a high budget.

Oddly this is inverted by a species encountered by Voyager that look sufficiently lizard like but turn out to be, while not human, from Earth!

In Stargate SG-1 and Stargate Atlantis, the "humans" in Pegasus and the Ori galaxy were seeded by the Ancients through genetic engineering, and are not directly descended from them, despite the use of the term "ancestors" in Pegasus. The humans on Earth presumably came about the same way. Humans were not seeded on any other Milky Way planet, the Goa'uld brought them to those worlds from Earth.

The four alien kids from Roswell who looked human, but prettier. It's gradually established that they are actually traditional Roswell greys in human form. The thing is, they assumed these forms before exploring outside their crashed spaceship as children. The reason they knew to do so was later Handwaved by explaining they are Half Human Hybrids. Whew!

There were several races that basically looked like humans or Sebaceans, except with strange colored eyes or hair or (sometimes) skin. They could be Sebacean renegades (like the ones in "Look At the Princess"), but it's rarely clarified. It is rather strange that John is constantly mistaken for a Sebacean, and not, say, a Litigaran.

Subverted somewhat as it is revealed in the peacekeeper wars that the Sebaceans actually *are* humans, just genetically engineered to a much higher level of evolution.

Mork, from Mork and Mindy. He was even able to have a kid with Mindy (although he was the one who laid the egg, and the kid was middle-aged Jonathan Winters.)

Power Rangersreally abuses this trope, invoking it for more or less anyone who isn't a rubber-forehead-alien or a robot-ish thingy. They even stated that aliens can be human, but they never explained how the same species can exist in multiple planets.

"What, you think Earth is the only place humans come from?" -Andros in his first appearance

The Centauri from Babylon 5 look outwardly exactly like humans, except for their barely noticeable Cute Little Fangs. They also have distinctive hairstyles - the men wear their hair in fans like peacock tails and the women shave their heads - but this is a cultural difference rather than a physical one.

However, beneath the surface they have Bizarre Alien Biology - double hearts, lack of major blood vessels in the wrists, and very different genitalia (the men have six Naughty Tentacles and the women have six orifices along their spines).

This was lampshaded in the first episode, where it is revealed that, after encountering humans for the first time, the sneaky Centauri claimed that their physical similarity was due to Earth being a long-forgotten Centauri colony. Human scientists, no doubt keeping the fossil record in mind, got hold of some Centauri DNA and disproved this claim. The Centauri saved face by claiming "clerical error" had mislabelled Earth as a lost colony.

The aliens on 3rd Rock from the Sun mention a few times that they've taken on human form and describe their natural form as being "purple tubes". They seem to have picked their human bodies from a catalogue.

Vicki's son Eric, fathered by the Big Giant Head in his human guise, looks like a perfectly ordinary human baby and is rejected by the tabloids because Vicki didn't even try to make him look more "alien".

Pax and Crona from At The End Of The Milky Way both look human, but with three differences—they constantly crave sugar, their hair changes color depending on their emotions, and they make quick, pig-like noises when they're upset. Strangely enough, only Pax shows the two last signs, leading one to believe that it's either an Informed Ability for Crona, or he's just so slick he never changes emotion from 'groovy'.

The aliens in The Event are distinguished from humans only by their longer lifespans and certain undescribed "skeletal and serological abnormalities". The latter are pronounced enough that a blood test will reveal them, and one plants himself with a tube of human blood to avoid arousing suspicions during a blood test. A DNA test will also reveal them, and dogs sometimes bark at them.

So you're watching Blake's 7 and you find yourself wondering whether the very-human looking primitive tribe on this episode's guest planet are alien humanoids or descendants of a lost human colony? Don't bother thinking about it that hard. The series itself even lampshaded this in the 4th season:

Vila: Everyone came from Earth originally. That's a well-known fact.Soolin: It's a well-known opinion, actually.Tarrant: Most well known facts are.

Animorphs did this most of the time with Ax and Visser Three, for budget reasons. It was a *lot* more common than the books.

Cole and possibly (but not for certain) Zin in Tracker. The rest were alien life forces inhabiting human bodies.

In the recent Syfy version of Flash Gordon, Flash calls the inhabitants of Mongo "aliens" even though they look entirely human and even (inexplicably) speak English.

The Hitchhiker's Guide to the Galaxy has several examples, most notably Ford and Zaphod's unnamed species from the Betelgeuse system (the latter's extra head and arm are due to surgery). The only known differences are biological incompatibility with humans and multi-centennial lifespans.

Super Robot Wars: Original Generation reveals that all the Human Aliens are actually humans, who left Earth long ago voluntarily. The Mysterious Lovecraftian Aliens refer to Earth as the "Land of Beginning", where sentient life first evolved.

Galactic Civilizations II has a race called the Altarians, who are essentially Humans With Psychic Powers. The Altarians even call the Terrans their "lesser cousins." It's implied in the backstory, however, that the two races might have a common origin.

That being said, the game makes it clear they are two separate species, and unlikely to be compatible for reproduction (no one has really tried).

Star Control II is mostly pretty good about making its aliens different from humans, though there are still a suspiciously large number of bipeds with heads on the top. However, one species, the Syreen, are your typical blue-skinned space babes - and they comment on the perplexing similarity between their species (the big difference being matriarchal rather than patriarchal). They're so close, in fact, that they're apparently sexually compatible, capable of producing fertile offspring. It is implied in the game's rich backstory, however, that it's because a certain other alien species transplanted some ancient Syreen to Earth as part of an extremely long-term experiment.

Similarly, the Lunarians in Final Fantasy IV don't look too different from humans other than slightly different skin tones and hair colors. They can even interbreed with humans and the two major characters are Half-Lunarian.

The D'ni in Myst count, as they evolved on a different planet. Up until URU introduced the Bahro, all sentient inhabitants of D'ni-linked worlds were humanoid, suggesting that some part of their linking technology automatically avoids creating links to worlds with non-humanoid inhabitants for some reason.

There is some precedent for such an interpretation, even given the Bahro. D'ni law (although not any actual aspect of The Art) required all ages to conform to certain environmental conditions, for safety reasons. Since these conditions fostered the evolution of the D'ni, it stands to reason that they would foster the evolution of biologically similar races, especially if they were sufficiently constrained.

Going along with Star Wars above, Knights of the Old Republic has several. Juhani looks like a human with tattoos and an odd accent, the Handmaiden (and by extension the entire Echani species) look like humans with whitehair and silver eyes (and can interbreed with humans), Visas and Miraluka in general look exactly like humans until you remove their hoods (they don't have eyes), and there is a Zeltron minor character on Telos near the beginning.

Note that many Star Wars species are actually 'near-Humans', meaning that they are descended from Humans but evolved into something else because of long-term genetic isolation. This is because before the Hyperdrive was invented, people traveled around in generation ships or sleeper vessels; some limited interspecies contact occurred, but no organization on the scale of the Republic or Empire was possible. Also, not all isolated Human populations diverged genetically if their new environment was benign enough; for example, the inhabitants of Naboo stayed well within the Human genetic range, but diverged from mainstream humanity culturally. Apparently, Indians are an aberration.

While not referred to as aliens, many of the demons from Disgaea fall under this, since we see that they do inhabitant different planets throughout space.

Escape From St Marys: You first think you're looking for a shriveled green man, for your search's actual result turns out more like this.

The Tautiq, a race of alien refugees who now live on earth in the Global Guardians PBEM Universe, basically look like taller, thinner humans with odd hair-and-skin color combinations. They aren't "sexually compatible" with humans, either, but you can't tell that without seeing them naked.

The Pelkons, another group of alien refugees who now live on earth are even more human-like than the Tautiq, (the primary difference are leopard-like spots on their chests and backs and milk-white, pupilless eyes), as they are "sexually compatible" (but are not cross-fertile) with humans.

Almost all characters in Chaos Fighters are this. The exceptions are Irtial and Muranyl, who are from Earth.

In Atomic Betty, Betty Barrett is an alien girl from the planet Bane of Fragnog.

In Ben 10 Alien Force, Alan is a Pyronite crossbreed who looks human except for when he's using his powers, and it's revealed that Gwen is a Half-Human Hybrid and gets her powers from her alien grandmother (the logical extension is, of course, that anyone without an Omnitrix strapped to their wrist who has powers is an alien or part-alien. The fans have had fun with this).

Word Girl is an alien from the planet Lexicon, but looks nothing remotely exotic.

But it's not surprising considering that in the Eva universe, humans were descended from the 2nd Angel, Lilith. As such, one of the aforementioned Half Human Hybrids (Kaworu) refers to humanity as "Lilim". Then in End of Evangelion Misato puts forth the theory that humanity, collectively, is the 18th Angel.

Although books are naturally far less vulnerable to this trope than Live Action TV, given that it takes significantly less effort to write a character as a "20-foot arachnid" than it does to act said spider.

Prot in K-PAX explains this by saying that it is the most energy efficient form to take on Earth. Of course, he may or may not be an alien.

In the earlier film which might have inspired the novel, an Argentinian production called Hombre Mirando al Sudeste (Man Looking Southeast), Rantes explains to the doctor that though they came in a ship, he and the others are actually physical projections from a distant, doomed future on another planet, and that they naturally adapt to whatever the observer expects to see. Of course, he may not be an alien, either--though he does have Psychic Powers, and his equally-alien (?) female friend does leak blue liquid from her mouth when excited, and then again, he also claims to be The Messiah...yeah, it's one hell of a Mind Screw.

Both the Transformers & the Brave Series have a weird variation on this, wherein there are several planets besides Cybertron/whatever planet the heroes come from that are inhabited by intelligent Transforming Mecha. Sometimes explained as being colonies of the main characters' race, sometimes not. While it may be reasonable to assume that a sufficiently advanced civilization would discard their weak organic bodies for more durable mechanical ones, the whole transforming thing is pushing it. The weirdest example being the Japanese Beast Wars II series, where there is a planet of highly evolved Funny Animal-like aliens who have developed to the point of Trans-funnyanimalism, where they have upgraded themselves with cybernetics. This allows them to turn into humanoid robot forms that look uncannily like the Maximals & Predacons, despite having no prior contact with them, for no apparent reason other than Rule of Cool.

Mostly averted in the Star Wars series. It does feature a few human-looking (possibly) aliens, although those may just be human colonies. It also features plenty of Rubber Forehead Aliens. But then there are also many species that are very non-human-looking. It's a richly diverse galaxy.

Subverted in Galaxy Quest, as the aliens initially appear human, but are using technology to change their appearance because their true form is . . . unsettling.

Subverted in the remake of The Day the Earth Stood Still; Klaatu's human form is implied to have been grown inside his initial containment suit to allow him to be compatible with the Earth's environment.

Averted in the novel Quest by Andreas Eschbach, when it is explained that: 1.All human races originated on earth and just evolved differently due to different environments. 2.All of the galaxy's life originated on one planet and cells of it have been spread by comets.

Averted in the novel Transformers: Ghosts of Yesterday (a prequel to the film), where Starscream claims that any sufficiently advanced race would naturally build machines that were similar to Cybertronians, as the Decepticons believe that they are the most perfect lifeforms in the galaxy. However, he also may have been simply trying to explain away the fact that the human spaceship Ghost 1 seemed to be built using Cybertronian technology (i.e. that Megatron, the Decepticons' true leader, has been found).

Conspicuously and consciously avoided in Wayne D. Barlowe's illustrated sci-fi novel Expedition. Barlowe, a noted fantastic fiction illustrator who darn well knows his biology, openly despises this trope and so he invented an alien race who is very like humankind in their attitude and culture - but they look a bit like a cross between a hot air balloon and an airborne octopus.

In Larry Niven's Ringworld series, there are various humanoid races who all turn out to be descended from the same race of Precursors who are the ancestors of Earth humans.

The Martians and Venusians of S.M. Stirling's The Lords of Creation novels look human because they are (more or less); the eponymous beings, in prehistoric times, Terraformed Mars and Venus and seeded them with Earth life (repeating the process several times, so that on Venus you have humans sharing the planet with dinosaurs and mammalian megafauna).

The aliens in Robert Zubrin's The Holy Land consider themselves the humans, and the Earthlings merely 'proto-humans'. Given their superior senses, telepathic ability, superior physiques, and superlative hygiene, they're probably right. However, they themselves originated on Earth, about twenty thousand years ago.

Some of the Doctor Who Expanded Universe novels have the Doctor come across as mildly not-so-human, to generally creepy effect. Anji seems to be particularly prone to noticing this. In one scene, when he does strike her as a convincing human, she considers him "a fake" and refers to him as "the alien" and "it" before she remembers he is, after all, her friend and a nice guy. In another scene, they'd have really run up the special effects budget if it were TV, just to make people go "Jesus Christ, ewwww" at the protagonist:

In Hugo’s arms, the Doctor hung bonelessly limp, as if he might suddenly flow to the floor in a puddle. Anji had never seen a human body sag like that; no human being had that sort of muscular-skeletal frame. For a frightened instant, she felt more kinship with the man with no limbs[1] than she did with the Doctor.

Averted in the Sector General series. Sure, they have one species of Human Alien, but they have seventy species total, so that is to be expected eventually. There are also species which look nothing like humans but look a lot like each other, inverting the trope.

Animorphs pointedly averts this trope. The most humanoid alien ever mentioned in the series is a species of amphibious monkey. Also, the Hork-Bajir feature basically the same head/two arms/two legs body shape, but otherwise go even beyond Rubber Forehead Aliens (in fact, they more closely resemble dinosaurs. The torsos of Andalites look fairly human, and the head has a Rubber Forehead Alien quality to it, but otherwise they are very different (having a basic body structure like that of a Centaur). Aside from those three, none of the alien races/species portrayed or mentioned in the books look anything even remotely human. Some of them even stray into Starfish Alien territory.

Babylon 5 had a strange inversion. The Vorlons are so alien looking that for the first two seasons we don't know how much of them is clothing and how much is their real body. Their true form appears to some kind of energy being, but every species perceives a Vorlon to look like their species version of an angel—it is suggested that this is the result of the ancient Vorlons having not only genetically tweaked the other species, but also appeared to them as angels at appropriate times in their respective development, creating a basis for the legends, taking advantage of them, or both.

It is also suggested that they have to telepathically maintain this illusion. This explains why Kosh claimed he had to rest after being see by so many the first time we see a Vorlon as an 'angel'. And why we eventually see their true forms, when the two Vorlons present are too occupied to care about the witnesses around them.

And, when we finally do see the (apparently) true form of Vorlons, it looks like a snake with feathered wings more than anything else, neatly covering a large swath of cultures that don't have anything resembling angels in their mythologies.

Firefly, a verse with Absent Aliens, pointedly avoids this trope. If the people on the next planet over look human, that's because they are.

Star Trek: The Next Generation had a weird variation once: apparently, it's not just humans that have doubles. "Who Watches the Watchers?" features a alien species that are physically identical to Vulcans (or at least Romulans, who are basically Vulcans with a ridge to make them distinct from their Federation cousins) without being a descendant. Strangely enough, they were apparently also mentally similar to Vulcans (the whole logic thing).

Subverted in an episode of The Twilight Zone in which astronauts are surprised to find Mars inhabited by human beings.

Lampshaded when a Turian, Salarian, and Human are having an Asari dance for them at a bachelor party. The Turian and Human wonder why they both find Asari attractive even though turians and humans look so different. The human says that asari resemble humans very closely, but the turian points out their head ridges and comments that he thinks asari look like blue turians to him. The human wonders if the asari are using their innate biotic powers to subconsciously mind control the other races into finding them more attractive, and the turain shoots this down with a simple "Shut up, you'll ruin asari for me." Even the Salarian is interested (and again notes the similarity to his own race), which is especially notable since Salarians have no sex drive.

Salarians may have no sex drive, but it is shown (mostly in the second game, where the race is more prominent) that Salarians do understand and show love. Of particular note is the Salarian with an Asari daughter in one of the games market hubs.

Played with with Quarians as well. As an unmasked Tali reveals, their faces are nigh identical to humans, with the exception of having different eye colors, but the rest of their anatomy is very different, like having three claw like fingers instead of hands, bowed legs, and more pronounced sexual dimorphism (ie, men have huge chests, women have large hips), in addition to having completely different DNA and biochemistry. Still, Quarians and Humans are very similar, and easily the two species closest in appearance in the entire series.

Alien Dice has numerous examples of aliens who look similar to humans but with subtle differences, such as exotic Hair Colors or Cute Little Fangs. It also has a rather interesting subversion when it is revealed that the reason that the blueskinned Rishan look human is because they are human, having been created using genetic material taken from Earth humans generations ago.

El Goonish Shive. Aliens and magical beings get around by wearing T-shirts that say "Human" or some such. (One person notices that his coworker is an alien. Her denying it is enough to convince the others, and she and this coworker wind up sending silly notes back and forth to each other about it.) Of course, Uryuoms being natural shapeshifters and the creators of Transformation Ray technology, they could hide by simply becoming human. Of course, that wouldn't be funny.

Two of them hire Ted (seen in a flashback) to design human forms for them, and provide the technology for it - apparently there are legal/political/religious reasons why they can't do it themselves, rather than an inability to do it themselves. Also, once they've been raygunned into humans, they can (implied) shift back and forth freely.

Captain Crandall of Teamo Supremo claims to be from another planet, despite the fact that he looks too much like his "Earth-mom" to possibly not be her child.

In Winx Club, most of the people there are like this except with the notable exception of the Big Bad of Season 2, Lord Darkar.

Subverted in Monster Buster Club; Cathy seems like a Human Alien at first glance... but various lines indicate that this is just a human disguise like we see on other aliens in the series, and her true form hews closer to the Starfish Aliens trope.